A. Field Of The Invention
The present invention relates to recombinant DNA technology. More specifically it relates to a means of determining from restriction fragment hybridization patterns whether a gene polymorphism associated with improved milk production is present in a bovine cell.
B. Description Of The Art
With the competitive pressures that the dairy industry is facing, there has been significant interest in breeding and selecting dairy cattle which have improved milk production characteristics. Significant improvements have been achieved using standard breeding techniques in which progeny are studied. Their production results are then used to guide further breeding. One particularly successful family (from a milk production standpoint) is the Holstein line deriving from Carlin-M Ivanhoe Bell (registration number 1667366, Holstein-Friesian Association, Brattleboro, Vt.). It has been estimated that currently more than 25% of the highest total performance index Holstein bulls in the U.S. are progeny of this individual.
Unfortunately, such standard techniques require years to evaluate the true genetic value by progeny testing each bull. During progeny testing, many cows must be bred and give birth to offspring. The females must be raised, bred, allowed to give birth and, finally milked for a minimum length of time. The costs of confirming that a particular bull has superior genetics is therefore very high.
Given the problems involved in using standard selection techniques, some have tried to improve milk production by locating genes that express proteins important to milk production, cloning them, and then adding commercially produced amounts of these proteins to feeds, drugs, and the like. Various bovine genes have in fact been shown to express proteins that are important for the control of mammary growth, lactogenesis, and/or lactation. One of these, bovine prolactin, is approximately 10 kilobases (kb) in length. See S. Camper et al., 3 DNA 237-249 (1984). Unfortunately, there has been significant political and regulatory resistance to the introduction of such methods.
Various other research has discovered that polymorphisms (change in the genetic code) can be associated with recognizable differences in restriction fragment lengths of certain portions of the human genome. This has been of value in creating an assay for certain genetic diseases in humans. See e.g. D. Botstein et al., 32 Am. J. Human Gene. 314-331 (1980).
Polymorphisms which do not affect amino acid composition have been reported adjacent to the bovine prolactin gene. These bovine prolactin studies have generally focused on differences around these loci between breeds or among individuals of an undetermined relationship. To date, applicants are unaware of anyone else having successfully located any polymorphism associated with a bovine gene which is indicative of improved milk production.
Thus, it can be seen that a need exists for a means of more efficiently selecting and breeding cattle for the trait of improved milk production.